The Sound of the Sea
Vol.6. 19th June 2017
Guest post by Claire Lacey
Claire comes to the RRS Discovery with 15 years, and 35,000 nautical miles, of marine mammal survey experience, using both acoustic and visual survey methods. Based at the Sea Mammal Research Unit at the University of St Andrews, Claire works primarily on the SCANS-III project, looking at the abundance and distribution of whales and dolphins throughout the European Atlantic.
Cetaceans (whales and dolphins) live in an environment where it is often very dark and turbid which can make it difficult to navigate, communicate or find food effectively. As a result, they are often highly vocal, producing a variety of different sounds which can be used for both navigation and foraging (echolocation) and communication. Scientists from the Sea Mammal Research Unit (SMRU) at the University of St Andrews – working in collaboration with Gisli Vikingsson at the Marine and Freshwater Research Institute in Reykjavik, Iceland – are able to use the sounds made by the cetaceans themselves to provide clues as to what species are to be found in this area, and their density and distribution. To do this, we are towing passive acoustic monitoring (PAM) equipment.
Pilot Whales © Marguerite Tarzia
An underwater recording studio…
The equipment is made up of a hydrophone array containing three different underwater microphone elements. This is towed 200m astern of the ship and can stay out even in really bad weather and overnight, allowing us to collect cetacean data throughout the trip. We are making recordings continuously at a rate of 500,000 samples per second, and after we get back to the lab at the end of the trip, we will process these to look for the vocalisations of whales and dolphins.
The CTD: this device samples water for oceanographic information, e.g. conductivity, temperature, depth © Marguerite Tarzia
Sound and Vision
Collecting acoustic data can be a very useful addition to collecting visual observation information as it allows us to detect the presence of animals even when we can’t see them – for example at night, in fog or in poor sea conditions, when visual observations are difficult (and we’ve had plenty of those this trip so far!).
Marguerite Tarzia (centre left) & the whale team © Marguerite Tarzia
There are also some species which spend a considerable amount of their time underwater – deep diving species. They are underwater for so much of the time that they can be rarely seen at the surface. But since they vocalise, we are able to detect them even if we haven’t seen them. One example of a species like this is the sperm whale. These animals can dive for over an hour – during which time they cannot be seen by observers. However, when they dive, they produce loud, clear clicks throughout their time underwater. These can be detected and localised to find out the animals’ distribution and density.
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